Adenovirus vectors have shown promise for vaccines, but one key hurdle is preexisting immunity to these viruses in humans. The VRC has been investigating the use of priming with either DNA or adenovirus vaccines and the use of alternate adenoviral serotypes or modified adenoviral vectors to overcome prior immunity. During the past year, the VRC has evaluated chimpanzee adenovirus vectors (ChAd3 and ChAd63) to analyze their ability to induce an immune response as compared to Ad5 and in the presence of Ad5 seropostivity. Several of these vectors are being further tested to evaluate their potential use in clinical trials. Plans are in progress to produce cGMP lots of a ChAd HIV vaccine.